Tinning long strips



Patented Aug. 1, 1933 UNITED STATES PATENT OFFICE mums LONG s'rmrs No Drawing. Application November 11, 1930 Serial No. 495,002

7 Claims.

invention relates to a process for applying a protective coating to sheet metal and, in particular, to the coating of ferrous strips in long conthe actual tizming operation itself as now prac-- ticed characterized by certain undesirable rep suits. when it is attempted to coat ferrous strip continuoush the first few feet of the strip that go through the bath are properly coated with tin, making a product which is perfect in all respects.

After the first length of a few feet of perfect strip has gone through the tinning bath, however, an

imperfection shows up in the strip in the form of a streak of scrufi adhering to the sheet and spoiling the continuity of the perfect finish thereof.

g Scruff an alloy of tin and iron which results from the partial solution of the iron in the strip in the mclten tin of the bath. This alloy collects between the finishing rolls of the usual tinning device at intervals, it is gathered up between the rolls and the strip and is spread on the latter to fem the defective portion hereinabove mentioned. This problem is not encountered in the of sheets because the pinch rolls roll the scrufi toward the list edge or drip edge on the 1 end or" the sheet to which the scrufi ad- I hares after passing through the rolls. In the tinning of strip, however, the scruff collects between the rolls and finally becomes sufdciently pasty to be taken through the rolls and spread on the to form a blemish on the surface thereof.

The formation of the alloy constituting the scruff can, of course, not be prevented and it is, in fact, a desirable phenomenon since it is very useful in forming the well known tenacious bond a between the pure tin and the iron of the base. The

problem, therefore. is to get rid of the alloy which collects between the rolls as it is removed from the portion of the strip which comes out perfect.

3 here invented the method of tinmng strip substantially the equipment now in use for this purpose. In accordance with the invention, 1 reverse the direction of rotation of the pinch rolls which draw the strip through the tinning 0 bath, intermittently during the tinning process.

I also provide for agitating the palm oil floating on the molten tin at the same time. The scruff collecting between the pinch rolls is thus scattered in the palm oil and the agitation'of the latter causes it to settle down to the bottom of the molten tin as does the scruff that is formed continuously where the molten tin is in contact with the iron pot.

In this way, the scruff will be prevented from collecting to such an' extent that it is taken up between the rolls and spread over the strip to form a blemish on the latter. The reversal of the pinch rolls need not be carried very far. A reversal of the forward movement of the strip as muchas may be sufficient to cause the 8.0- cumulated scruff to be dissipated in the palm oil throughwhich it can sink to the bottom of the pot. No time will be lost by reversing the rolls to this small extent asofte'n as may be necessary to prevent the undesired accumulation of scruff '7 between the rolls. The strip may be reversed for every few feet of its travel and the operation of reversal may be made practically instantaneous.

Any suitable automatically operated apparatus may be employed for intermittently reversing the pinch rolls through a small angle.

By reversing the pinch rolls intermittently during the tinning of the strip, the accumulated scrufi will be deposited in the pot and will not be picked up by the strip passing through the rolls. As a result, the entire length of the strip possesses the smoothness and perfection of finish of the coating which characterizes the sheets tinned by the present method and the first few feet of a strip which has been subjected to the as usual tinning process. By reversing the rolls, the scruff or tin-iron alloy collected between the rolls is removed therefrom so that it may be disposed of and so prevent its being picked up by the strip.

Although I have described herein only one method of carrying out the process, it is obvious that the invention is capable of other modes of use. Any changes in the invention as described may, therefore, be made without departing from the spirit of the invention as defined by the following claims.

I claim:

1. In a method of tinning continuous steel strips which includes the steps of drawing the strip through molten tin and between a pair of pinch rolls, and intermittently reversing the di rection of rotation of the rolls.

2. The method of tinning long strips by drawing them through a tinning bath between pinch rolls, which includes the step of periodically reversing the direction of rotation of said rolls for a short period.

3. In the art of tinning sheet metal by passing it through molten tin and between pinch rolls,

the step of reversing the rotation of the rolls through a small angle at intervals.

4. In a method of tinning by passing strip through a bath and between finishing rolls, the

5 step of stopping the rolls intermittently and reversing their direction of rotation.

5. In a method of preventing the adhesion of scruff to long lengths of strip during tinning, the step of intermittently reversing the movement of the strip through a short distance.

'6. A method or tinning a strip including the ABRAM P. S'IECKEL. 

